The aforementioned application points out that earlier methods of making dental prostheses, e.g. crowns, plates and replacement teeth, involved a multiplicity of steps, many of which required intervention in the mouth of the patient.
Not only was the patient required to attend the dental practitioner a comparatively large number of times but frequently the intervention was painful, especially during the fitting stages.
In the formation of a dental crown, for example, the operations include the grinding of the tooth to be replaced in order to obtain a truncated stump, the taking of an impression of the stump using an elastomeric path in order to obtain a mold whose hollow part has a shape which is complementary to that of the stump, the casting of plaster into said mold in order to obtain a reproduction of the stump, the preparation of the crown in wax taking into consideration adjacent and antagonistic teeth (a process which was generally highly subjective and the effect of which required high skill and long years of experience by the practitioner), the positioning of the crown in a coating cylinder, the melting out of the wax, the injection of molten metal to replace the wax, stripping and polishing of the metal crown, and, setting of the crown on the stump.
In spite of the fact that these numerous operations were carried out by highly skilled and fastidious dental surgeons, frequently modification of the prosthesis was required after the formation.
Indeed, because of the large number of steps which were involved and the fact that even with mechanical impressions, accurate fits could not be ensured, and because the relationship of each prosthesis to the adjacent and antagonistic teeth was something which had to be gauged subjectively by the practitioner, the production of a dental prosthesis hitherto seldom could be accomplished without the many visits mentioned previously. Indeed, in spite of numerous fitting operations, there was always the danger that the finished prosthesis would cause discomfort to the patient.
Another disadvantage of the earlier systems should also be apparent. For example, the metals used had to be fluid or malleable at easily obtainable temperatures. The numerous steps required the intervention of a laboratory and skilled practitioners at different stages in addition to the dental surgeon. The equipment required overall, including an oven, sand-blasting machine, inserting equipment, contributed substantially to the cost of producing the prosthesis.
Because the temperature to which the materials were subjected, ranged from room temperature at which some work was done to the casting temperature, to the body temperature of the patient, uncontrolled thermal expansion posed a problem.
In the production of other prosthesis, it was necessary to utilize a so-called "bloody impression" when, for example, an impression was required from injured bone. This involved pain and required especially sterile surgical procedures and handling of the impression media. Obviously, repeated fits here were an even more severe drawback.